In Sacco Degradability of Protein (N) and Dry Matter in Samples of Individual Feeds or Combinations; Tested with Diets Medium or High in Protein

Two rumen cannulated dairy cows were fed diets of grass silage and barley meal (diet MP) and grass silage, barley meal and soya-bean meal (diet HP). Samples of soya-bean meal (SBM), fish meal (FM), barley (B) and grass silage (S, freeze dried), and mixes of two samples (S+B, S+SBM, S+FM, B+SBM, B+FM, SBM+FM) were incubated in nylon bags (in sacco) in the rumen for 3, 6, 12 and 24 h. In connection with the in sacco measurements rumen samples were collected and pH, ammonia and volatile fatty acids (VFA) were determined. In general N and dry matter (DM) disappearance in sacco was greatest on diet HP. The exception was the N disappearance from samples B, FM and FM+S which was more or less unaffected by the diet fed. Both the N and DM disappearance for the mixes generally agreed well with predictions made from degradation results for the single feeds. Within sample, the N and DM disappearance correlated closely. The effective rumen degradation of feed protein (EPD) was calculated at three chosen rumen outflow rates (i.e. 3, 5 and 7%/h). By increasing flow rate the effect on EPD was most accentuated on diet MP. The changes in rumen degradability was accompanied with changes in rumen fermentation. The average pH, ammonia level (mmol/l) and the ratio C2+C4/C3 was 6.7, 4.1 and 4.44 on diet MP and 6.8, 15.0 and 3.78 on diet HP respectively. The results are discussed in relation to other data.